1. Center for Access and Delivery Research and Evaluation, Iowa City Veterans Affairs Health Care System , Iowa City, Iowa , USA
2. Division of Infectious Diseases, University of Iowa Carver College of Medicine , Iowa City, Iowa , USA
3. Department of Biostatistics, University of Iowa , Iowa City, Iowa , USA
4. VA Greater Los Angeles Healthcare System , Los Angeles, California , USA
5. David Geffen School of Medicine at the University of California , Los Angeles, California , USA